Abstract
• Unique relationship between Intrinsic threshold stress intensity, ΔK th,i and near-tip residual stress, σ*, carries an important implication. • Given LEFM considerations, K max , K op and ΔK th,i will be uniquely related to σ* under constant amplitude loading. • Analytical relationships are provided to derive both ΔK th,i versus K max and associated K op at threshold. • Results for a steel and titanium alloy show that cracks can grow at much lower ΔK than is seen in laboratory testing. • The described procedure provides ΔK th data applicable to naturally forming cracks and pre-existing defects. An analytical procedure is described that connects crack opening stress intensity, K op , with maximum stress intensity, K max , associated with threshold conditions under constant amplitude loading. The underlying theory is based on the experimental finding that closure-free intrinsic threshold stress intensity, ΔK th,i , is solely related to a certain computed near-tip residual stress, σ*. The proposed procedure enables extrapolation of ΔK th to lower values of maximum stress intensity, K max that cannot be reproduced by prevailing testing practice. It is demonstrated on experimental threshold data from a naval steel and a titanium alloy.
Published Version
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